1. Field of the Invention
The present invention relates to illumination systems, and in particular to illumination systems wherein a light source is scanned across a targeted area at a rapid speed such that the entire illuminated pattern appears to be simultaneously illuminated by the light source.
2. Brief Description of the Related Art
Using conventional portable and fixed illumination devices, such as a flashlight or an automobile headlamp, respectively, the light that is cast onto a target is brightest in the center, and loses intensity as it reaches the outside of the light pattern generated by the light source. Such illumination devices usually employ parabolic reflectors to direct the light from the bulb to the targeted area to be illuminated. When the bulb is located at the focus of the parabolic reflector, the light rays leaving the bulb and impacting on the surface of the reflector will travel the same distance as they emerge parallel to the axis. This arrangement results in a bright and concentrated circular-shaped beam, with areas of lower illumination at the periphery of the beam. Such illumination devices must be physically re-positioned toward a particular section of the targeted area in order to strike such section with the brightest point of the light source.
In order to form a broader beam with typical illumination devices, the light bulb is moved within the parabolic reflector so that the bulb is no longer at the focus. The light rays leaving the bulb now reflect off of the parabolic surface and emerge diverging from the axis. The circular-shaped broader beam formed in this manner is less bright by at least the increase in the beam area over the spot, and it will have a non-illuminated spot at the center of the broad beam. This resultant broad beam creates a non-ideal illumination pattern on objects that are to be illuminated. In many conventional flashlights, the user may manually adjust between the tight, circular beam and a broader beam as described herein by applying a twisting motion at the flashlight head, thereby re-positioning the bulb with respect to the reflector.
Some prior attempts to create a broad beam and eliminate the non-illuminated portions of a flashlight's beam of light have included flashlights constructed with complex reflectors including multiple parabola; flashlights constructed with multiple light sources and control circuitry; and flashlights constructed with a light source that moves within the reflector. Examples of flashlights that employ some of the above techniques are described in U.S. Pat. Nos. 4,984,140 and 5,367,446 to Ellion. These patents teach a rapidly changing combination of a broad beam and a spot beam by moving either the light source in relation to a parabolic reflector, or moving the parabolic reflector in relation to the light source, to illuminate over the usually non-illuminated area. The undue complexity of these designs leads to unacceptably high manufacturing costs and to issues of reliability associated with their operation.
Other attempts to produce wide-area illumination devices have employed motors and galvanometers to physically move the parabolic reflector or light source. U.S. Pat. No. 3,865,790 to Du Shane teaches a lighting mechanism that spins horizontally in a 360 degree angle. U.S. Pat. No. 4,797,796 to Eastman, II, et al. teaches a device that oscillates or shakes the parabolic reflector, causing the beam of light to scan a horizontal area. The physical wear on the components, motors, and gears, and the power supply necessary to power the motors and galvanometers, render such designs unpractical for most extended-use purposes.
In addition to prior art that manipulates the parabolic reflector and light source by the use of motors, other attempts have been to manipulate the light beam only. One method to scan a beam is well known as used in supermarket scanners. A rotating hexagon with mirrored surfaces causes the light to be scanned across a targeted area in a one-dimensional pattern. One patent that teaches a system based on this process is U.S. Pat. No. 5,954,416 to Peterson. While casting a broad beam, the hexagon in such devices rotates, and the changing light pattern minimizes a dark area of the beam from the flashlight as the changing pattern directs light rays across the dark area. This one-dimensional spinning scanner can only minimize the typically non-illuminated area, while still only generating a weaker broad beam, and produces the standard problems with physically whirling, motorized mechanisms.
Another attempt at scanning a light source's beam is illustrated in U.S. Pat. No. 4,363,085 to Demas, which provides a vehicle headlamp wherein one or more reflectors scan a collimated beam of light to generate a desired light beam pattern and project it onto the road. In one method, the scanning reflector is actuated by a pair of coil-motor transducers that are coupled to the scanning reflector by ball-and-socket connectors. These actuators move the scanning reflector in two dimensions. A second embodiment uses galvanometric oscillating motors to scan a collimated beam of light in two dimensions and project it onto the road. A pulley system may be tied to the housing of the vehicle headlight to change the overall angle of the device. This design is not intended for portable use, is encumbered by the usual downfalls of spinning and mechanical motors, and requires a non-economical and impractical power supply.
A relatively new device for controlling light beams is available in the form of the digital micro-mirror array. These devices are variously classified as micro-electro-mechanical systems (MEMS) and micro-opto-electro-mechanical systems (MOEMS). Innovations in movie projection systems, such as with the Texas Instruments DLP micro-mirror array device, are now well known in the industry. Color projection display systems utilizing such devices as the DLP system have very high resolution and millions of gray-scale levels, so they can display fine nuances of comparative shades. Many other companies are competing with Texas Instruments with their own designs of reflective arrays. These systems in general are designed to accept the data from an image processor and to use that data to control the on/off stages of the millions of mirrors in their array, to reflect only the desired amount of light for each pixel of the picture image presented by the digital video signal. Simply speaking, this is accomplished by turning the individual mirror for a specific pixel on and off very rapidly. When a mirror is switched on more often than off, a light gray pixel is reflected. When a mirror is switched off more often than on, a dark gray pixel is reflected. Rapid switching allows up to 1024 shades of gray reflections in commercially available devices. In this fashion, the digital video signal entering the system gets converted into a highly detailed grayscale image. Elements of the grayscale image are then fed through a color wheel or some similar mechanism to add color to the gray-scale projection. These devices are usually very expensive, rarely portable, and are designed to reflect a large spot-beam of light back onto a screen, blocking or partially blocking chosen pixel-size elements to project black and gray-scale spots in those chosen pixel areas. Such devices are not beam-steering systems, as known in the industry, but are devices that offer on/off tilt-control of individually addressable micro-mirrors in a large array. Such systems or devices, when all of their arrayed mirrors are aligned in an on or off position, are similar to a solid mirror or a solid non-reflective surface having an overall area of their combined mirrors. In the case where all of the millions of mirrors are reflecting the light source onto a screen, it is analogous to bypassing their system entirely and shining the original light source onto the screen, or reflecting the light source onto the screen using a simple one-piece mirror. In either case, the intensity of the light would not be suitable for an illumination device and the cost of the accompanying electronics would be prohibitive for most illumination applications.
Another example of an application of a beam-steering device is well known in laser projection systems such as in an observatory, where shaded and translucent drawings are projected for such purposes as “laser light shows.” Most often, two single mirrors are controlled by separate galvanometers. Such systems are usually a fixed system, having many large components, requiring high voltage, AC power, and computer control. Some systems exist that use a two-dimensional micro-mirror device to eliminate the use of the galvanometer motors, but these systems are generally considered fixed systems designed to project line drawings, and are not usable for general illumination applications.
The limitations of the prior art are overcome by the present invention as described below.